1. Field of the Invention
The present invention relates generally to a connection box for fusible links. More particularly, the present invention relates to a connection box employable for at least two kinds of fusible links each having different exterior dimensions to be used for the purpose of protecting a power supply source circuit. Further, the present invention relates to a terminal nut to be secured to a connection box of the foregoing type.
2. The Prior Art
Various kinds of fusible links each having different exterior dimensions corresponding to a rated electric current have been hitherto practically used for a vehicle such as an automobile or the like. Particularly, a plurality of fusible links each usable for the purpose of protecting electrical circuits in an automobile and having different dimensions have been used corresponding to plural kinds of rated electric currents per each automobile. In the circumstances as mentioned above, it is necessary that at least two kinds predetermined dimensions are inevitably prepared for a connection box for fusible links having lead wires attached thereto to make electrical connection between a battery supply source and an electrical equipment. This fact will readily be understandable by making dimensional comparison between a small-sized connection box accompanied by a fusible link and a large-sized connection box accompanied by a fusible link with reference to FIG. 1 and FIG. 3. Incidentally, FIG. 1 shows by way of perspective view a small-sized connection box and a fusible link to be received in the latter, and FIG. 3 shows by way of perspective view a large-sized connection box and a fusible link to be received in the latter.
Prior to detailed description, general structure of a connection box and a fusible link to be received in the latter will briefly be described below. In FIG. 1 and FIG. 3, reference characters Ca and Cb designate fusible links, respectively. The fusible link Ca is composed of a parallelpiped-shaped housing 110a molded of a synthetic resin and having an inverted U-shaped fuse received therein, two feet 122a made of an electrical conductive material and extending downward of the housing 110a in parallel with each other, and a transparent cover 112a fitted onto the upper end of the housing 110a. Likewise, the fusible link Cb is composed of a parallelpiped-shaped housing 110b molded of a synthetic resin and having an inverted U-shaped fuse received therein, two feet 122b made of an electrical conductive material and extending downward of the housing 110b in parallel with each other, and a transparent cover (not shown) fitted to the upper end of the housing 110b. With respect to the small-sized fusible link Ca as shown in FIG. 1, inverted U-shaped cutouts 123 are formed at the lower end parts of the feet 122a. After the fusible link Ca is inserted into a connection box 103a, the feet 122a are placed on bosses b each having a female-threaded hole formed therethrough on central walls I as if the fuse is bridged between both the bosses b. In addition, terminals A of lead wires connected to a power source and an electrical equipment are located in alignment with the female-threaded holes formed through the bosses b, and subsequently, bolts D are inserted through the terminals A and threadably fitted into the female-threaded holes, whereby the terminals A are firmly secured to the central walls I to make electrical connection between both the lead cables via the fuse.
As typically shown in FIG. 2 that is a vertical sectional view of an assembly of the housing 103a and the fusible link Ca as shown in FIG. 1, the connection box 103a is designed in the parallelpiped-shaped configuration. Basically, a ceiling plate H and central walls I extending downward of the bottom surface of the ceiling plate H at the central part of the latter are made integral with each other, and two cavities are defined by a peripheral wall F and a partition wall G in such a manner as to allow fusible links Ca having exterior dimensions coincident with interior dimensions of each cavity to be snugly received in the cavities. In addition, two pairs of slots E each extending in parallel with each other are formed through the bottom surfaces of the cavities, i.e., the upper surface of the ceiling plate H so as enable the feet 122a of the terminal to be inserted therethrough. This means that the thickness of the central wall I should be set to be smaller than a distance between each pair of slots E.
The structure of the small-sized fusible link Ca and the large-sized fusible link Ca and the connection boxes 103a and 103b as shown in FIG. 1 and FIG. 3 has been described above. In this connection, in case of the large-sized fusible link Cb shown in FIG. 3, circular holes f formed through the feet 122b of the fuse corresponding to bosses b are substituted for the inverted U-shaped cutouts 123 of the small-sized fusible link Ca shown in FIG. 1. Thus, in practical use, the bosses b cooperate with the circular holes f. As shown in FIG. 1 and FIG. 3, each of the feet 122a and 122b of the fusible links Ca and Cb has a substantially inverted U-shaped sectional contour, and the opposite ends of each foot are inwardly bent at a right angle to form ribs 2. Each of the feet 122a and the feet 122b is dimensioned to have a width smaller than the width of each slot E.
While the aforementioned structure of the fusible links Ca and Cb and the corresponding connection boxes 103a and 103b is taken into account, exterior dimensions of the small-sized fusible link Ca and the connection box 103a will be compared with those of the large-sized fusible link Cb and the connection box 103b below with reference to FIG. 1 and FIG. 3.
A distance Z.sub.1 between two feet 122a of the small-sized fusible link Ca shown in FIG. 1 is dimensionally coincident with a distance Z.sub.2 between two feet 122b of the large-sized fusible link Cb shown in FIG. 3. Next, when an effective length P.sub.1 of the foot 122a of the small-sized fusible link Ca as measured from the center of the boss b toward the housing 110a is compared with an effective length P.sub.2 of the foot 122b of the large-sized fusible link Cb as measured from the center of the boss b toward the housing 110b while each fusible link is fitted into the corresponding connection box, the former is smaller than the latter.
Next, when the connection box 103a for the small-sized fusible link Ca is compared with the connection box 103b for the large-sized fusible link Cb, a transverse width X.sub.l of each cavity of the connection box 103a for the small-sized fusible link Ca as measured in parallel with a pair of slots E shown in FIG. 1 is smaller than a transverse width X.sub.2 of each cavity of the connection box 103b for the large-sized fusible link Cb as measured in parallel with a pair of slots E shown in FIG. 3. However, a length Y.sub.1 as measured at a right angle relative to the transverse width X.sub.1 is dimensionally coincident with a length Y.sub.2 as measured at a right angle relative to the transverse width X.sub.2.
In addition, a length x.sub.1 and a transverse width y.sub.1 of the peripheral wall F of the connection box 103a for the small-sized fusible link Ca are smaller than a length x.sub.2 and a transverse width Y.sub.2 of the peripheral wall F of the connection box 103b for the large-sized fusible link Cb. Thus, the dimensional relationship between the small-sized fusible link Ca and the large-sized fusible link Cb can be represented by inequalities of P.sub.1 &lt;P2, X.sub.1 &lt;X.sub.2, x.sub.1 &lt;x.sub.2 and y.sub.1 &lt;y.sub.2. P As is apparent from the above description, each conventional connection box is required to have dimensions corresponding to a fusible link to be fitted thereinto in terms of an effective foot length of the fusible link and a transverse width of a housing of the same. Especially, in case of a small-sized passenger car, a plurality of connection boxed are arranged in a narrow space in the passenger car. For this reason, there is a possibility that each fusible link fitting operation is achieved with many manhours due to the dimensional difference among a plurality of fusible links, and moreover, an insert portion of each fusible link is damaged or injured when each fusible link is fitted into the corresponding connection box. In addition, it is obvious from the viewpoint of production that a plurality of injection molding dies are prepared corresponding to the number of kinds of the fusible links, resulting in the conventional fusible links being disadvantageously employed not only from the viewpoint of a production cost of each conventional fusible link but also from the view, point of each fusible link fitting operation to be achieved at a high efficiency.
FIG. 4 shows by way of fragmentary sectional view the contour of the foot 122b of the large-sized fusible link Cb shown in FIG. 3 while the foot 122b is inserted through the slots E. As the fusible link Cb is repeatedly attached to and detached from the connection box 103b, a certain play appears between each rib e of the fusible link Cb and the corresponding side wall of the connection box 103b due to repeated rubbing operations achieved therebetween. Consequently, there is a possibility that the inverted U-shaped cutout 123 or the circular hole f is not exactly located in alignment with the boss f on the connection box side, whereby there may arise an occasion that the terminals of lead wires can not correctly be connected to each other via the fusible link, resulting in satisfactory electrical connection failing to be made between a supply source and an electricity consumer side.
Therefore, with the conventional connection box 103a, 103b constructed in the above-described manner, there arises a necessity for individually preparing a connection box corresponding to dimensions of each fusible link to be fitted thereto, i.e., an effective foot length P and peripheral wall lengths X and Y of the housing 110a, 110b wherein the foregoing dimensions vary depending on an electric current capacity of each fusible link.
In case that a plurality of connection boxes are arranged in a narrow space on a vehicle body, a wide space is inevitably required. Another problems are such that each fusible link fitting operation is achieved with many manhours due to dimensional difference among a plurality of fusible links, insert portions of each fusible link are readily damaged or injured, and a die cost associated directly with a production cost for each connection box is largely increased due to a necessity for preparing a plurality of injection molding dies.